1. Field of the Invention
The present invention relates to electronic circuits, and in particular relates to a phased-array device and a calibration method therefor.
2. Description of the Related Art
A phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in phases and gains relationship that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions. Corresponding to the each antenna there is a transmitter and receiver responsible for managing the phases and gains relationship of the respective signal feeding in the antenna. The phased array can utilize digital techniques for antenna beamforming, which modify phases and amplitudes of digital signals by digitally multiplying a complex weight to each antenna feed. The signals from all elements are then combined digitally in such a way that signals at particular angles experience constructive interference while others experience destructive interference, giving a number in digital form whose directional response is a function of the array geometry and the manipulated digital signals, resulting in a controllable beamforming shape. Each antenna element feeds a dedicated receiver channel element, providing amplification and selectivity. The frequency and phase responses of the receiver channel elements must track closely, over the full dynamic range of signals to be handled.
To obtain the full benefit of a digital beamforming array it is necessary to calibrate out all phase and gain mismatches of the system. The calibration routine contains injecting a test signal into each receiving channel element in turn, and measuring the amplitude and phase of the received signal. Any departures from the desired amplitude and phase can then be compensated using corrected digital weights. The performance in the presence of channel element mismatches is critical parameter of any phased array. These variations result in amplitude and phase mismatches in the radiated/received signals and hence adversely affect the beam pattern. The mismatch may arise from the intra-chip variation inherent to any process technology.